Lubricant compositions



United States Patent 3,303,131 LUBRICANT COMPOSITIONS Hans Low, Bonn, Germany, and Russell L. Booher, Ed-

wardsville, and John E. Lauek, Godfrey, Ill., assignors to Shell Oil Company, New York, N.Y., a corporation of Delaware N0 Drawing. Filed Dec. 11, 1964, Ser. No. 417,811

17 Claims. (Cl. 25247.5)

This invention relates to synthetic ester lubricant compositions containing a novel antioxidant combination. In particular, it relates to ester lubricating oils containing a combination of certain amides of aminopyridines and certain organic amines.

Synthetic lubricants have gained recent prominence in the field of lubrication because of stringent requirements of long life under extreme conditions imposed by certain low as -65 F-. -to as high as 450 to 500 F. for said applications. I

Althoughthese synthetic ,lubricants are more stable than mineral oils, they nevertheless undergo oxidation when exposed to air, especially when subjected to elevated temperatures such as occur under normal operation. Oxidation stability is further impaired by dissolution of metals under operating conditions. Dissolved metals seem to catalyze oxidative degradation of the lubricant, thereby substantially shortening its useful life. Additives have traditionally been employed in small concentrations to impart resistance to oxidation to these lubricants. Much research eifort has been directed to finding additives or combinations of additives which are eifective antioxidants for long periods of time yet which do not impart or cause undesirable side effects such as sludge and deposit formation, increased corrosion, viscosity change, discoloration, and so on. Available information regarding mineral oil formulation is generally of little aid in developing successful synthetic lubricants since entirely different side effects are likely to occur under the more extreme conditions to which synthetic lubricants are subjected.

It is known to use various aromatic and heterocyclic amines as additives to increase oxidation stability of synthetic lubricants. These amines are often used alone or in combination. For example, Eickemeyer, US. 3,121,691, February 18, 1964, teaches the use of a combination of phenyl-alpha-naphthylamine with an amino quinoline,'an aminopyridine, or a dipyridylamine to reduce oxidation.

The present invention provides a synthetic lubricant having superior oxidation stability imparted by a combination of (A) an amide of an aminopyridine from the group consisting of ice where R is an alkyl or aryl group having 1 to about 20 carbons, preferably 2 to 12 carbons, and R is an alkylene or arylene group having from 2 to about 20, preferably 2 to 12 carbons, and (B) an organic nitrogen-containing antioxidant which is preferably an organic amine. These lubricants have extremely good stability to oxidation, and also provide good cleanliness characteristics.

The amides of aminopyridines used as coadditives of the invention maybe amides of either 2-aminopyridine, 3-aminopyridine, or 4-aminopyridine. The 2- and 4-sub stituted compounds, especially 4-substituted, are preferred. Appropriate concentration of these compounds are from .05 to 5%, preferably 0.1 to 3%, especially 0.1 to 1% by weight of the final lubricating composition. Examples of amides which are used in combination with organic amines are N-4-pyridylpelargonamide, N-2-pyridylpelargonarnide, N-4-pyridylvaleramide, N-4- pyridylacetamide, N-3-pyridylvaleramide, N-4-pyriclylbenzamide, N-4-pyridyltoluarnide, N,N di 4 pyridyladipamide, N-Z-pyridyl-N'-4-pyridylsebacamide, N,N-di- 2-pyridylphthalamide, N,N di-4 pyridylisophthalamide, etc. These additives are well-known compounds which may be prepared by addition of the appropriate carboxylic acid to an aminopyridine,

Organic amines..to be used .in combinationwith the above-described amides are primary Ito tertiary organic amines'having from 4 to 12 carbon atoms, preferably containing no elements other than carbon, hydrogen, nitrogen, and sulfur. Preferred amines contain from 4 to 12 carbons, 0-to 2 nitrogens', and 0 to 1 sulfur atoms. They may be aryl amines, diaryl amines, heterocyclic amines, or thiodia'rylamines. These compounds are beneficially present in an amount of from about .05 to 5%, preferably 0.1 to 3% by weight of the final lubricating composition. Amounts of about 1.0% are preferred. Examples of suitable aryl amines are naphthyl amine and octylphenylamine. Examples of suitable diaryl amines are phenyl-a-naphthylamine, phenyl B naphthylamine, B,fl-dinaphthylamine, ogfl-dinaphthylamine, and diphenylamine. Examples of suitable heterocyclic amines are 2-aminopyridine, 4-aminopyridine, 2,2-dipyridylamin'e', 4,4-dipyridylamine, 2,4'-dipyridylamine, 2,6-diaminopyridine, phenyl-Z-pyridylamine, and naphthyl-Z-pyridylamine. Examples of suitable thiodiarylamines are phenothiazine, phenylthio-alpha-naphthylamine, and phenylthio-beta-naphthylamine. Preferred amines are diarylamines, especially phenyl-alpha-naphthylarnine and diphenylamine.

To illustrate the efficacy of the additive combination of the invention, air oxidation tests were conducted on samples of various ester-base lubricants. The tests were carried out at 450 F. by passing a stream of air at the rate of milliliters per minute through a ZO-gram sample of the appropriate ester fluid. To more closely approximate actual operating conditions, 20 ppm. each of iron or iron and copper, as indicated, were added as octoates. The base stock for all tests was a mixture of 67% C -C acid esters of pentaerythritol and 33% C -C acid esters of dipentaerythritol. Runs 13-19 were conducted in the additional presence of an extreme pressure additive to illustrate that the unexpected interaction of the amide and the amine persists in the presence of an additional additive; this is important because additional additives may give rise to problems of incompatibility among additives. The EP agent used was a salt of monochloromethylphosphinic acid and C primary amines (referred to in the table as MCMPA).

Results 'of the air-oxidation tests are shown in Table 1 below. Oxidation stability is determined by the length of time, known as the induction period, before which a significant increase in the rate of oxygen absorption occurs.

TABLE I Introduction period, hr. Run No. Additives, percent \v. Catalysts Fe Fe+Cu 1.0 phenothiazine (PTZ) 1 1.0 pheuyl-a-napthylaniine (PAN) l 2 1.0 diplienylamine (DPA) 3 0.5 2, 2- lipyridylamine (2, 2-DPA) 1 1 0.2 MCMPA 0 0.5 N--pyridylpelnrgonamide.. 0 1 1.0 PAN 0.5 2, 2-l) PA 3 1.0 DPA 0.5 2, PA 1.0 PAN 0.5 N-4-pyridylpelargonami 12 1.0 DPA 0.5 N-4-pyridylpelargonamide 14 1.0 PAN 0.5 N-4-pyridylvaleramide. 23 1.0 DPA 0.5 N-5-pyridylvaleramid 13 1.0 PAN 0.5 N-4-pyridylacetamide 16 1.0 PAN 0.2 MGMPA 5 1.0 PAN +0.5 N-2-pyridylpelargonamide+0.2

MCMPA 7 4 1.0 PAN+0.5 N-4-pyridylpelargonamide+0.2 26 MCMPA 15 26 1.0 DPA+0.5 N-4-pyridylpelargonamide+0.2

MCMPA 6 21 1 0 PAN-l-O 5 N-4-pyridylvaleramide+0.2

MCMPA 27 1.0 DPA|0.5 N-4pyridylvaleramide+0.2

MCMPA 1.0 PAN+0.5 N,N-di-4-pyridyladipamide+ 0.2 MCMPA 1.0 PTZ+0.5 N-4-pyridylvaleramide+0.2

MCMPA 17 17 22. 0.5 2, 2-DPA+0.5 N-4-pyridylvaleramide+0.2

MCMPA 1 25 An examination of Runs 1-6 indicates that additives of the invention, when used individually, are relatively ineffective under the stringent test conditions. A comparison of Runs 9-13 with Runs 7 and 8-shows that combinations of the invention are considerably more effective even than known synergistic antioxidant combinations. Runs 15-22 illustrate that the cooperative effect of amides and amines of the invention persist in the presence of a known EP agent.

Several compositions of the invention were tested in the Type 2 Bearing Test. This test is used as a final method of evaluating high-temperature synthetic lubricants prior to full scale jet engine testing. It utilizes a circulating oil system and a 100 mm. test bearing similar to many of the bearings usedin jet engines. The test is of 100 hours duration and is conducted at 440 F. tank temperature, 400 F. oil-in temperature, and 500 F. bearing temperature. During the test, oil flow to the test bearing is controlled at 600 ml./ min. Saturated air enters the bearing compartment at 0.30-0.35 ft. /min. and is scavenged with the test oil to a Z-gall-on test oil tank. Performance of the oil is judged on the basis of resulting deposits and increase in acid number and viscosity. Results of tests of two oils of the invention follow in Table 2. The test oils compared favorably with other available known formulations.

TABLE II.-TYPE II BEARING TEST RESULTS Composition, percent w.:

Base A 1 N-4-pyrid rlvolermnide 1 Copper dibutylditliiocnrbalnnte 1 C -C acid esters of pentaerytliritol.

2 0 -010 acid esters of dipentaerythritol.

3 Salt of monocliloromethylpliosphonic acid and mixed C1sC;z primary amines.

4 The amount of this and the subsequent additives present in the compositions is expressed as percent based upon the total weight of Base A and Base B.

Cal

Suitable synthetic lubricant base stocks for the practice of the invention are esters of alcohols having 1 to 20, especially 4 to 12 carbons and aliphatic carboxylic acids having from 3 to 20, especially 4 to 12 carbons. The ester base may comprise a simple ester (reaction product of a rnonohydroxyalcohol and a monocarboxylic acid), a polyester (reaction product of an alcohol and an acid, one of which has more than one functional group), or a complex ester (reaction product of a polyfunctional acid with more than one alcohol, or of a polyfunctional alcohol with more than one acid). Also, excellent synthetic lubricants may be formulated from mixtures of esters, such as major proportions of complex esters and minor amount-s of diesters.

Monohydric alcohols suitable for making ester base stocks include methyl, butyl, isooctyl, dodecyl and octadecyl alcohols. Oxo alcohols prepared by the reaction of olefins with carbon monoxide and hydrogen are suitable. Neo-alcohols, i.e., alcohols having no hydrogens on the beta carbon atom are preferred. Examples of such alcohols are 2,2,4-trimethylpentanol-l and 2,2-dimethyl propanol.

Polyaloohols used for the production of base oil esters preferably contain 1 to 12 carbons. Examples of dialcohols are 2-ethyl-1,3-hex-anedio1, 2-propyl-3,3-heptanediol, 2-butyl-1,3-butanediol, 2,4-dimesityl-l,3 butanediol, and polypropylene glycols having molecular weights of from about 100 to 300. Alcohols having 3, 4, 5 or more hydroxyl groups per molecule are also suitable and are preferred; examples of these polyols are pentaerythritol, dipentaerythritol, and trimethylolpropane. Mixtures of alcohols may also be used.

Suitable carboxylic acids for making the ester base oils include monoand di-basic aliphatic carboxylic acids. Examples of appropriate acids are butyric, valeric, sebacic, azelaic, suberic, succinic, caproic, adipic, ethyl suberic, diethyl adipic, oxalic, malonic, glutaric, pentadecanedicarboxylic, diglycolic, thiodiglycolic, acetic, propionic, caprylic, lauric, palmitic, pimelic, and mixtures thereof. Preferred acids are sebacic, azelaic, glutaric, adipic, and their mixtures.

Examples of suitable ester base oils are ethyl palmitate, ethyl laurate, butyl stearate, di-(2-ethylhexy) sebacate, di-(Z-ethylhexyl) azelate, ethyl glycol dilaurate, di-(2- ethylhexyl) phthalate, di-(l,3-methylbutyl) adipate, di- (l-ethylpropyl) azelate, diisopropyl-oxylate, dicylcl-ohexyl sebacate, glycerol tri-n-heptoate, di(undecyl) azelate, and tetraethylene glycol di-(Z-ethylene caproate), and mixtures thereof. An especially preferred mixture of esters consists of about 50 to wt. bis(2,2,4-trimethylpenyl) azelate and 20 to 50% Wt. 1,1,1-trirnethylyl propane triheptanoate.

Especially preferred esters for use as base stocks in the present invention are esters of .monocarboxylic acids having 3 to 12 carbon-s and polyalcohols such as pentaerythritol, dipentaerythritol, and trimethylolpropane. Examples of these esters are pentaerythrityl butyrate, pentaerythrityl tetrabutyrate, pentaerythrityl tetravalerate, pentaerythrityl tetracaproate, pentaerythrityl dibutyratedicaproate, pentaerythrityl lbutyratecaproate divalerate, pentaerythrityl butyrate trivalerate, pentaerythrityl butyrate tricaproate, pentaerythrityl tributyratecaproate, mixed C -C saturated fatty acid esters of pentaeryt-hritol, dipentaerythrityl hexayalerate, dipentaerythrityl hexacapro- 0 ate, dipentaerythrityl hexaheptoate, dipentaerythrityl hexacaprylate, dipentaerythrityl tributyratecaproate, dipentaerythrityl trivalerate .trinonylate dipentaerythrityl mixed hexaesters of C -C fatty acids and trimethylolpropane heptylate. Pentaerythrityl esters of mixtures of C -C acids are excellent base oils, and are commercially available from Hercules Chemical Company.

Ester oils may be prepared by simple reaction of the alcoholic and acidic reactants in proportions suitable for producing the desired product; preparation preferably takes place in a solvent such as an aromatic hydrocarbon,

and in the presence of a catalyst, such as HCl, HF, HBr, H 80 H PO SCCl BF etc. Preparation of suitable esters is described in Eickemeyer, U.S. 3,038,859, issued June 12, 1962, and Young, U.S. 3,121,109, issued February 11, 1964.

Compositions of the invention may also contain other additives to further improve properties of the oil. Examples of other such additives are EP agents, viscosity index improvers, anticorrosion agents, detergents, etc.

Some specific embodiments of the compositions of the invention are as follows:

Composition 1 Base A: Percent weight Bis(2,2,4-trimethy1pentyl) azelate 60 1,1,l-trimethylpropane triheptanoate 40 Phenyl-a-naphthylamine l N-4-pyridylpelargonamide 0.5 Salt of mixed C C primary amines and monochloromethylphosphonic acid (MCMPA) 0.2

Composition 2 We claim as our invention: 1. A lubricating composition comprising a major amount of a synthetic ester base oil and (1) 0.05 to 5% by weight of an amide selected from the group consisting of and wherein R is selected from alkyl and aryl having from 1 to about carbons, and R is selected from alkylene and arylene having from 2 to about 20 carbons, and

(2) 0.05 to 5% by weight of an amine selected from the group consisting of arylamines, diarylamines, heterocyclicamines and t-hiodia-ryla-mines having from 4 to 12 carbon atoms;

2. The composition of claim 1 wherein the organic amine is a diarylamine.

3. The composition of claim 1 wherein the organic amine is a thiodiarylamine.

4. The composition of claim 2 wherein the diarylatmine is selected from the group consisting of phenyl-u-naphthylamine and diphenylamine.

5. A lubricating composition comprising a major amount of a synthetic ester base oil and 6 (1) 0.1 to 3% by weight of an amide selected from the group consisting of and wherein R is selected from alkyl and aryl having from 1 to about 20 carbons, and R is selected from alkylene and arylene having from 2 to about 20 carbons, and

(2) 0.05 to 5% by weight of an amine selected from the group consisting of arylamines, diarylamines, heterocyclicamines and thiodiarylamines having from 4 to 12 carbon atoms.

6. A lubricant composition comprising a major amount of a synthetic ester base oil and (1) 0.01 to 3% by weight of an amide of the formula wherein R is selected from the group consisting of alkyl and aryl having from 1 to about 20 carbons, and

(2) 0.05 to 5% by weight of an amine selected from the group consisting of arylamines, diarylamines, heterocyclicamines and t-hiodiarylamines having from 4 to 12 carbon atoms.

7. The composition of claim 6 wherein the pyridyl group is substituted in the 2-position.

8. The composition of claim 6 wherein the pyridyl group is substituted in the 4-position.

9. The composition of claim 6 wherein the amine is diarylamine.

10. A lubricant composition comprising a major amount of a pentaerythrityl ester base oil, and

(1) 0.01% to 3% by weight of an amide selected from the group consisting of if NH-O-R and o o n NH-O-R -b-NH wherein R is selected from alkyl and aryl having from 1 to about 20 carbons, and R is selected from alkylene and arylene having from 2 to about 20 carbons, and

(2) 0.05 to 5% by weight of a diarylamine.

11. The composition of claim 10 wherein the diaryl amine is phenyl-a-naphthylamine.

12. The composition of claim 10 wherein the amide is N-4-pyridylpelargonamide.

13. The composition of claim 12 wherein the diarylamine is phenyl-a-naphthylamine.

14. The composition of claim 12 wherein the diarylamine is diphenylamine.

15. The composition of claim 10 wherein the amide is N-4-pyridylvaleramide.

'16. The composition of claim 15 wherein the diarylamine is pihenyl-a-naphthylamine.

17. The composition of claim 15 wherein the diarylamine is diphenylamine.

References Cited by the Examiner UNITED STATES PATENTS Tierney et a1 252-403 X Eickemeyer 25 25 1.5 X Hotten 252-515 X Oberrig-ht et al. 252-515 X DANIEL E. WYMAN, Primary Examiner.

10 P P. GARVIN, Assistant Examiner. 

1. A LUBRICATING COMPOSITION COMPRISING A MAJOR AMOUNT OF A SYNTHETIC ESTER BASE OIL AND (1) 0.05 TO 5% BY WEIGHT OF AN AMIDE SELECTED FROM THE GROUP CONSISTING OF 